Internally insulated pipes for the transport of high temperature fluids, e.g. gases or liquids, generally are constituted of a metallic material which must be protected from the fluid transported through the pipe against overheating. This is especially the case in nuclear reactor applications where failure of the metallic member of the pipe may be detrimental to the environment, to operating personnel and to the equipment of the nuclear reactor.
This is particularly the case when the hot fluid is under pressure and the passage of the hot fluid through the pipe places the latter under substantial stress or loading.
In general, the internally lined pipes used heretofore for such purposes are formed internally with ceramic foils or fibrous material, as well as solid ceramic linings, the latter being especially useful for reinforced concrete vessels or ducts.
Ceramic inner linings of pipes and other vessels have hitherto encountered two basic problems.
Since it is desired that the lining create a significant temperature gradient between its internal surface and its external surface surrounded by the metallic conduit, significant tension stresses develop along the outer or cold side of the insulation which frequently cannot be withstood by the ceramic material and thus there is a tendency for cracks to form in the ceramic material. The danger of such crack formation with ceramic internal linings for conduits and the like is especially pronounced when the temperature gradient is very high and it has been proposed to avoid such crack formation by subdividing the ceramic internal lining into a plurality of segments. However, when such segments are used, there is a possibility that gas will pass through the spaces between the segments or along the interfaces between adjoining segments and thus reduce the reliability of the insulation and the insulation effectiveness.
Even where such segments are not provided, there is always the danger that the fluid will flow between the inner insulation and the outer wall of the lined duct. Such undesired gas flow also adversely affects the insulation efficiency and is frequently uncontrollable so that locally high temperatures may be experienced at the outer wall of the pipe and may be detrimental to the latter, affecting the useful life of the pipe. In addition, unpredictable forces may develop at the outer metallic pipe wall which can cause rupture thereof, especially if temperature fluctuations cause degradation of the metal material.